Polylogarithmic Descent for Almost All Collatz Orbits in Natural Density

We prove that, in ordinary natural density, almost every positive integer admits a shortcut Collatz iterate of polylogarithmic size within logarithmically many steps, while every iterate up to the same witness remains at most n^(1+beta) for every fixed beta > 0. The result supplies an explicit critical polylogarithmic exponent, quantitative exceptional-set rates, a logarithmic witnessing clock, critical log-log refinements, and stretched-logarithmic companion results.

The proof counts parity words exactly on dyadic shells. Large-scale prefix bounds control orbit height, a terminal odd-step tail controls short blocks that time out, and decreasing thresholds convert every later failure into a direct first passage of the original orbit. This organizes long multi-landing passages in natural density without a linear time-union loss: only O(sqrt(M log M)) cumulative passage times are possible.

A separate Lean 4 software record kernel-checks the formalized principal theorem chain. The formalization is supplementary; the manuscript proof is self-contained. All results are almost-all statements. The manuscript does not prove the pointwise Collatz conjecture or exclude exceptional cycles or divergent trajectories.